Carrier frequency interference detection device and method based on Wollaston prism

Abstract

The invention discloses a Wollaston prism-based carrier frequency interference detection device and a Wollaston prism-based carrier frequency interference detection method, which are characterized in that a Wollaston prism is used for separating reference light from test light at a small angle to realize carrier frequency, so that a return error generated by a method for introducing the carrier frequency by inclining a to-be-detected object at a certain angle originally is avoided; and high-precision carrier frequency interference detection is realized. The Wollaston prism is moved through the high-precision displacement table, so that the detection device can be compatible with carrier frequency interference detection and normal Fizeau interference detection. By designing the relay lens with the ultra-low return error, the return error in an interference detection light path is further reduced, and the detection precision is ensured. According to the invention, the dynamic carrier frequency interference detection of the surface shape of the to-be-detected object can be effectively realized with high precision.

Description

Technical Field

[0001] The invention belongs to the technical field of optical precision detection, and in particular relates to a carrier frequency interference detection device and method based on a Wollaston prism. Background Art

[0002] Carrier frequency interferometry uses the interference between test light and reference light at a certain angle, and realizes phase modulation by introducing a linear carrier frequency. Therefore, only one carrier frequency interferometry image is needed to realize phase extraction and obtain the surface shape information of the surface to be tested, which is suitable for real-time dynamic detection.

[0003] For example, the Chinese patent document with the publication number CN107560565A discloses a surface shape detection device and detection method based on dynamic time-sharing tilted carrier frequency interference. According to the surface shape of the detected element, the required spatial interference point source array position is calculated, and the time-sharing spatial interference point source array is generated by using the Tip / Tilt mirror. Each time the spatial posture of the Tip / Tilt mirror is adjusted, a spatial point source is arranged. Through the designed posture adjustment position, the scanning of the planned spatial point source is completed in sequence. The interference fringes are resolved to complete the surface shape reconstruction of the detected element, thereby realizing the surface shape measurement of the high-precision surface shape element of the present invention.

[0004] The current common method is to tilt the reference surface or the surface to be tested so that the test light and the reference light have a certain angle. In order to ensure that the low-frequency noise can be separated from the phase information through filtering and spectrum analysis technology, the reference surface or the surface to be tested needs to be tilted at a larger angle. However, due to the tilt of the reference surface or the surface to be tested, the path of the test light returning from the surface to be tested to the imaging surface is not exactly the same as the path of the reference light returning from the reference surface to the imaging surface. Each lens passing through the path will introduce different aberrations in the test light and the reference light. This deviation is called the return error. The existence of the return error will have a certain impact on the detection accuracy of the surface shape. When the tilt angle is small, the impact of the return error is relatively small. When the tilt angle is large, the impact of the return error on the detection result of the surface shape cannot be ignored. Especially when the system structure is more complex, the increase in the number of lenses will make the return error larger.

[0005] Therefore, a design is needed to avoid the influence of return error caused by the separation of the test light and the reference light. Summary of the invention

[0006] The present invention provides a carrier frequency interference detection device and method based on Wollaston prism, which can realize dynamic surface measurement with low return error and high precision.

[0007] A carrier frequency interference detection device based on Wollaston prism, comprising an interference measurement system and a computer processing module;

[0008] In the interference measurement system, the light emitted by the fiber laser is converted into linear polarized light after passing through the first polarizer, and is divided into S polarized light and P polarized light after passing through the polarization beam splitter prism; the S polarized light emitted from the polarization beam splitter prism passes through the first quarter wave plate, is reflected by the first plane reflector, is converted again by the first quarter wave plate into P polarized light, and then is incident on the third plane reflector; the P polarized light emitted from the polarization beam splitter prism passes through the second quarter wave plate, is reflected by the second plane reflector, is converted again by the second quarter wave plate into S polarized light, and then is incident on the third plane reflector; the P polarized light and S polarized light reflected by the third plane reflector pass through the beam expander and the first depolarization beam splitter prism, are expanded into parallel light by the focusing lens, the second depolarization beam splitter prism and the collimator, and then pass through the standard mirror and the sample to be measured;

[0009] The light reflected by the standard mirror is used as the reference light, and the light reflected by the sample to be tested is used as the test light; after the two beams of light pass through the collimator and the second depolarizing beam splitter prism again, one part is incident on the Wollaston prism through the second imaging mirror and emitted as two beams of light with a certain angle, which are imaged on the imaging camera after passing through the 1× relay lens group and the second polarizer; the other part passes through the focusing mirror and the first depolarizing beam splitter prism, and is imaged on the alignment camera through the first imaging mirror;

[0010] The Wollaston prism is mounted on a high-precision translation platform;

[0011] The computer processing module includes a displacement control module, an image acquisition module, and an interference pattern data analysis and processing module; wherein the displacement control module is used to control the movement of the high-precision displacement stage, and the image acquisition module is connected to the imaging camera to transmit data to the interference pattern data analysis and processing module for analysis and processing to obtain the surface shape information of the sample to be tested.

[0012] Furthermore, the fiber laser uses 532nm short coherent light.

[0013] Furthermore, the separation angle of the Wollaston prism is less than 2°.

[0014] Furthermore, the Wollaston prism is laterally moved by a high-precision translation stage to achieve compatibility between Fizeau interferometry and carrier frequency interferometry.

[0015] When the high-precision translation stage moves the Wollaston prism between the second imaging mirror and the 1× relay mirror group, the function of carrier frequency interference detection is realized; when the high-precision translation stage moves the Wollaston prism out of the carrier frequency interference optical path, the function of Fizeau interference detection is realized.

[0016] Furthermore, the 1× relay lens group includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens which are sequentially arranged on the same optical axis along the light propagation direction;

[0017] The first lens, the second lens, the third lens, the fifth lens, the sixth lens, and the seventh lens are symmetrically distributed with the fourth lens as the center.

[0018] Furthermore, the first lens and the seventh lens are both plano-convex lenses with positive power; the second lens and the sixth lens are both meniscus lenses with positive power; the third lens and the fifth lens are both biconcave lenses with negative power; and the fourth lens is a biconvex lens with positive power.

[0019] Furthermore, the optical path differences of the 1× relay lens assembly in the 1° field of view, 2° field of view, and 3° field of view are nearly consistent, and have an ultra-low return error.

[0020] Furthermore, the material refractive index of the first lens is 1.80 to 1.85; the radius of curvature of the front surface of the first lens is 34 mm to 35 mm; the rear surface of the first lens is a plane; the thickness of the first lens is 1 mm to 2 mm;

[0021] The material refractive index of the second lens is 1.80 to 1.85; the radius of curvature of the front surface of the second lens is 22 mm to 23 mm; the radius of curvature of the rear surface of the second lens is 45 mm to 46 mm; the thickness of the second lens is 2 mm to 3 mm;

[0022] The material refractive index of the third lens is 1.45 to 1.50; the radius of curvature of the front surface of the third lens is -117 mm to -118 mm; the radius of curvature of the rear surface of the third lens is 3 mm to 4 mm; the thickness of the third lens is 12 mm to 13 mm;

[0023] The material refractive index of the fourth lens is 1.50 to 1.55; the curvature radius of the front surface of the fourth lens is 4 mm to 5 mm; the curvature radius of the rear surface of the fourth lens is -4 mm to -5 mm; the thickness of the fourth lens is 6 mm to 7 mm;

[0024] The refractive index of the material of the fifth lens is 1.45 to 1.50; the curvature radius of the front surface of the fifth lens is -3 mm to -4 mm; the curvature radius of the rear surface of the fifth lens is 117 mm to 118 mm; the thickness of the fifth lens is 12 mm to 13 mm;

[0025] The refractive index of the material of the sixth lens is 1.80 to 1.85; the radius of curvature of the front surface of the sixth lens is -45 mm to -46 mm; the radius of curvature of the rear surface of the sixth lens is -22 mm to -23 mm; the thickness of the sixth lens is 2 mm to 3 mm;

[0026] The material refractive index of the seventh lens is 1.80-1.85; the front surface of the seventh lens is a plane; the curvature radius of the rear surface of the seventh lens is -34mm--35mm; and the thickness of the seventh lens is 1mm-2mm.

[0027] A carrier frequency interference detection method based on Wollaston prism, using the above carrier frequency interference detection method based on Wollaston prism, comprises the following steps:

[0028] Step 1, adjusting the posture of the standard mirror and the sample to be tested until the light spot reflected by the standard mirror and the sample to be tested in the alignment camera is located in the center and the light spot is the smallest;

[0029] Step 2, adjusting the distance d1 between the polarization beam splitter prism and the first plane reflector, the distance d2 between the polarization beam splitter prism and the second plane reflector, and the distance d3 between the standard mirror and the sample to be measured so that d1+d3=d2;

[0030] Step 3, adjust the position of the 1× relay lens to ensure that the two beams of light emitted from the Wollaston prism at a certain angle can completely enter the 1× relay lens group; at the same time, adjust the position of the second polarizer and the imaging camera until the interference pattern appears on the imaging camera.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The present invention uses a Wollaston prism to separate the reference light and the test light at a small angle to realize the carrier frequency, thereby avoiding the return error caused by the original method of introducing the carrier frequency by tilting the object to be tested at a certain angle, and realizing high-precision carrier frequency interference detection.

[0033] 2. The present invention moves the Wollaston prism by means of a high-precision translation stage, so that the detection device can be compatible with carrier frequency interferometry detection and normal Fizeau interferometry detection.

[0034] 3. The present invention further reduces the return error in the interference detection optical path by designing a relay lens with ultra-low return error, thereby ensuring detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a structural diagram of a carrier frequency interference detection device based on a Wollaston prism according to an embodiment of the present invention.

[0036] Figure 2 The figure is a schematic structural diagram of one embodiment of a 1× relay lens assembly provided by the present invention.

[0037] Figure 3 This is an optical path difference diagram of the 1× relay lens assembly provided by the present invention at 0°, 1° and 2° fields of view.

[0038] Figure 4Interference diagram of the 1× relay mirror assembly provided by the present invention under 0° field of view and 2° field of view. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0040] like Figure 1 As shown, a carrier frequency interference detection device based on Wollaston prism includes an interference measurement system and a computer processing module.

[0041] In the interference measurement system, the fiber laser 1 is used as the light source, and 532nm short coherent light is selected to ensure that only two beams of light can interfere and form an image in the end. The laser emitted by the light source is converted into linear polarized light after passing through the first polarizer 2, and is divided into two beams of light, P light and S light, after passing through the polarization beam splitter prism 3. The S light passes through the first quarter wave plate 4 and then reflects from the first plane reflector 5 and then passes through the first quarter wave plate 4 again. At this time, the S light emitted from the polarization beam splitter prism 3 is converted into P light. The P light emitted from the polarization beam splitter prism 3 passes through the second quarter wave plate 6 and then reflects from the second plane reflector 7 and then passes through the second quarter wave plate 6 again. At this time, the P light emitted from the polarization beam splitter prism 3 is converted into S light. By adjusting the spacing d1 between the polarization beam splitter prism 3 and the first plane reflector 5 and the spacing d2 between the polarization beam splitter prism 3 and the second plane reflector 7, there is a certain deviation in the phase of the P light and the S light when they are emitted from the polarization beam splitter prism 3 to the third plane reflector 8. The P light and the S light are expanded into a wide beam after passing through the beam expander 9, and converged into a spherical wave after passing through the first depolarizing beam splitter prism 10 and the focusing lens 13. The spherical wave passes through the second depolarizing beam splitter prism 14 and enters the collimator 15 to become parallel light. The parallel light hits the standard mirror 16 and the sample 17 to be tested, and then reflects through the collimator 15 and the second depolarizing beam splitter prism 14, and then turns through the second imaging lens 18 to become parallel light. The light incident on the standard mirror 16 and the sample 17 to be tested has a phase difference between the P light and the S light. After the two beams of light are reflected by the standard mirror 16 and the sample 17 to be tested, four beams of light with different phases will be returned, namely, the light reflected by the P light from the standard mirror 16, the light reflected by the P light from the sample 17 to be tested, the light reflected by the S light from the standard mirror 16, and the light reflected by the S light from the sample 17 to be tested. By adjusting the distance d3 between the standard mirror 16 and the sample 17 to make d1+d3=d2, the phase of the light reflected by the sample 17 and the light reflected by the standard mirror 16 can be interfered. The four beams of light are imaged on the imaging camera 23 through the Wollaston prism 19, the 1× relay lens group 21 and the second polarizer 22.

[0042] The light reflected from the standard mirror 16 and the sample to be measured 17 will be imaged on the alignment camera 12 through the first imaging mirror 11. The positions of the standard mirror 16 and the sample to be measured 17 can be adjusted according to the pattern on the alignment camera to facilitate subsequent interference measurement.

[0043] The Wollaston prism 19 can be removed from the interference optical path by using the high-precision translation stage 20, and the original optical path can be used for the function of Fizeau interferometry detection, thereby achieving the compatibility of Fizeau interferometry detection and carrier frequency interferometry detection.

[0044] The computer processing module includes a displacement control module, an image acquisition module, and an interference pattern data analysis and processing module; wherein the displacement control module is used to control the movement of the high-precision displacement stage 20, and the image acquisition module is connected to the imaging camera 23. After obtaining the carrier frequency interference pattern image of the interference imaging of the sample to be tested 17 and the standard mirror 16, the data is transmitted to the interference pattern data analysis and processing module for analysis and processing to obtain the surface information of the sample to be tested 17.

[0045] The method for performing carrier frequency interference detection using the above device is as follows:

[0046] Step 1, adjust the positions of the standard mirror 16 and the sample to be tested 17 until the light spot reflected by the standard mirror 16 and the sample to be tested 17 in the alignment camera 12 is located at the center and the light spot is the smallest.

[0047] Step 2, by adjusting the distance d1 between the polarization beam splitter prism 3 and the first plane reflector 5, the distance d2 between the polarization beam splitter prism 3 and the second plane reflector 7, and the distance d3 between the standard mirror 16 and the sample to be measured 17, d1, d2, d3 satisfy the following relationship:

[0048] d1+d3=d2

[0049] Step 3, adjust the position of the 1× relay lens (21) to ensure that the two beams of light emitted from the Wollaston prism 19 at a certain angle can completely enter the 1× relay lens group 21. At the same time, adjust the positions of the second polarizer 22 and the imaging camera 23 until the interference pattern appears on the imaging camera 23.

[0050] Figure 2 The design of the 1× relay lens group 21 in the device of the present invention is shown. The design includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens arranged in sequence on the same optical axis. The first lens, the second lens, the third lens and the fifth lens, the sixth lens, and the seventh lens are symmetrically distributed with the fourth lens as the center.

[0051] Among them, the first lens and the seventh lens are both plano-convex lenses with positive power; the second lens and the sixth lens are both meniscus lenses with positive power; the third lens and the fifth lens are both biconcave lenses with negative power; and the fourth lens is a biconvex lens with positive power.

[0052] Specifically, the material refractive index of the first lens of the 1× relay lens group is 1.80-1.85; the radius of curvature of the front surface of the first lens is 34mm-35mm; the rear surface of the first lens is a plane; the thickness of the first lens is 1mm-2mm; the material refractive index of the second lens is 1.80-1.85; the radius of curvature of the front surface of the second lens is 22mm-23mm; the radius of curvature of the rear surface of the second lens is 45mm-46mm; the thickness of the second lens is 2mm-3mm; the material refractive index of the third lens is 1.45-1.50; the radius of curvature of the front surface of the third lens is -117mm--118mm; the radius of curvature of the rear surface of the third lens is 3mm-4mm; the thickness of the third lens is 12mm-13mm; the material refractive index of the fourth lens is 1.50-1.55; the radius of curvature of the front surface of the fourth lens is 4mm- 5mm; the radius of curvature of the rear surface of the fourth lens is -4mm~-5mm; the thickness of the fourth lens is 6mm~7mm; the material refractive index of the fifth lens is 1.45~1.50; the radius of curvature of the front surface of the fifth lens is -3mm~-4mm; the radius of curvature of the rear surface of the fifth lens is 117mm~118mm; the thickness of the fifth lens is 12mm~13mm; the material refractive index of the sixth lens is 1.80~1.85; the radius of curvature of the front surface of the sixth lens is -45mm~-46mm; the radius of curvature of the rear surface of the sixth lens is -22mm~-23mm; the thickness of the sixth lens is 2mm~3mm; the material refractive index of the seventh lens is 1.80~1.85; the front surface of the seventh lens is a plane; the radius of curvature of the rear surface of the seventh lens is -34mm~-35mm; the thickness of the seventh lens is 1mm~2mm.

[0053] Figure 3 The optical path difference diagrams of the 1× relay mirror set at 0°, 1°, and 2° fields of view are shown. The optical path difference diagrams under the three fields of view are basically the same, showing that the designed 1× relay mirror set has ultra-low return error.

[0054] Figure 4 The interferogram of the 1× relay mirror set at 0° and 2° fields of view is shown. The PV value of the interferogram of the designed 1× relay mirror set at 0° and 2° fields of view is only 0.0041 wavelengths, which specifically shows that the designed 1× relay mirror set has ultra-low return error.

[0055] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A carrier frequency interference detection device based on Wollaston prism, characterized in that: It includes an interferometric measurement system and a computer processing module; In the interference measurement system, light emitted by the fiber laser (1) is converted into linearly polarized light after passing through a first polarizer (2), and is then divided into S-polarized light and P-polarized light after passing through a polarization beam splitter prism (3); the S-polarized light emitted from the polarization beam splitter prism (3) is passed through a first quarter-wave plate (4), is reflected by a first plane reflector (5), and is then converted again through the first quarter-wave plate (4) into P-polarized light, and is then incident on a third plane reflector (8); the P-polarized light emitted from the polarization beam splitter prism (3) is passed through a second quarter-wave plate (4), and is then reflected by a first plane reflector (5). After passing through a quarter wave plate (6), the P polarized light and the S polarized light are reflected by a second plane reflector (7), converted into S polarized light again by the second quarter wave plate (6), and then incident on a third plane reflector (8); the P polarized light and the S polarized light reflected by the third plane reflector (8) are passed through a beam expander (9) and a first depolarizing beam splitter prism (10), and then expanded into parallel light by a focusing lens (13), a second depolarizing beam splitter prism (14), and a collimator (15), and then passed through a standard lens (16) and a sample to be measured (17); The light reflected by the standard mirror (16) is used as reference light, and the light reflected by the sample to be tested (17) is used as test light; after the two beams of light pass through the collimator (15) and the second depolarizing beam splitter (14) again, a part of them is incident on the Wollaston prism (19) through the second imaging mirror (18), and is emitted as two beams of light with a certain angle, which are imaged on the imaging camera (23) after passing through the 1× relay lens group (21) and the second polarizer (22); the other part of the light passes through the focusing mirror (13) and the first depolarizing beam splitter (10), and is imaged on the alignment camera (12) through the first imaging mirror (11); The Wollaston prism (19) is mounted on a high-precision translation stage (20); The computer processing module comprises a displacement control module, an image acquisition module, and an interference pattern data analysis and processing module; wherein the displacement control module is used to control the high-precision displacement stage (20) to move, and the image acquisition module is connected to the imaging camera (23) to transmit data to the interference pattern data analysis and processing module for analysis and processing to obtain the surface shape information of the sample to be tested (17).

2. The carrier frequency interference detection device based on Wollaston prism according to claim 1, characterized in that: The optical fiber laser (1) adopts 532nm short coherent light.

3. The carrier frequency interference detection device based on Wollaston prism according to claim 1, characterized in that: The separation angle of the Wollaston prism (19) is below 2°.

4. The carrier frequency interference detection device based on Wollaston prism according to claim 1, characterized in that: The Wollaston prism (19) is moved laterally by a high-precision translation stage (20) to achieve compatibility between Fizeau interferometry detection and carrier frequency interferometry detection; When the high-precision displacement stage (20) moves the Wollaston prism (19) between the second imaging mirror (18) and the 1× relay mirror group (21), the function of carrier frequency interference detection is realized; when the high-precision displacement stage (20) moves the Wollaston prism (19) out of the carrier frequency interference optical path, the function of Fizeau interference detection is realized.

5. The carrier frequency interference detection device based on Wollaston prism according to claim 1, characterized in that: The 1× relay lens group (21) comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens and a seventh lens, which are sequentially arranged on the same optical axis along the light propagation direction; The first lens, the second lens, the third lens, the fifth lens, the sixth lens, and the seventh lens are symmetrically distributed with the fourth lens as the center.

6. The carrier frequency interference detection device based on Wollaston prism according to claim 5, characterized in that: The first lens and the seventh lens are both plano-convex lenses with positive focal power; the second lens and the sixth lens are both meniscus lenses with positive focal power; the third lens and the fifth lens are both biconcave lenses with negative focal power; and the fourth lens is a biconvex lens with positive focal power.

7. The carrier frequency interference detection device based on Wollaston prism according to claim 5, characterized in that: The optical path differences of the 1× relay lens group (21) in the 1° field of view, 2° field of view, and 3° field of view are nearly consistent, and have an ultra-low return error.

8. The carrier frequency interference detection device based on Wollaston prism according to claim 5, characterized in that: The material refractive index of the first lens is 1.80 to 1.85; the radius of curvature of the front surface of the first lens is 34 mm to 35 mm; the rear surface of the first lens is a plane; the thickness of the first lens is 1 mm to 2 mm; The material refractive index of the second lens is 1.80 to 1.85; the radius of curvature of the front surface of the second lens is 22 mm to 23 mm; the radius of curvature of the rear surface of the second lens is 45 mm to 46 mm; the thickness of the second lens is 2 mm to 3 mm; The material refractive index of the third lens is 1.45 to 1.50; the radius of curvature of the front surface of the third lens is -117 mm to -118 mm; the radius of curvature of the rear surface of the third lens is 3 mm to 4 mm; the thickness of the third lens is 12 mm to 13 mm; The material refractive index of the fourth lens is 1.50 to 1.55; the curvature radius of the front surface of the fourth lens is 4 mm to 5 mm; the curvature radius of the rear surface of the fourth lens is -4 mm to -5 mm; the thickness of the fourth lens is 6 mm to 7 mm; The refractive index of the material of the fifth lens is 1.45 to 1.50; the curvature radius of the front surface of the fifth lens is -3 mm to -4 mm; the curvature radius of the rear surface of the fifth lens is 117 mm to 118 mm; the thickness of the fifth lens is 12 mm to 13 mm; The refractive index of the material of the sixth lens is 1.80 to 1.85; the radius of curvature of the front surface of the sixth lens is -45 mm to -46 mm; the radius of curvature of the rear surface of the sixth lens is -22 mm to -23 mm; the thickness of the sixth lens is 2 mm to 3 mm; The material refractive index of the seventh lens is 1.80-1.85; the front surface of the seventh lens is a plane; the curvature radius of the rear surface of the seventh lens is -34mm--35mm; and the thickness of the seventh lens is 1mm-2mm.

9. A carrier frequency interference detection method based on Wollaston prism, characterized in that: The carrier frequency interference detection method based on Wollaston prism according to any one of claims 1 to 8 comprises the following steps: Step 1, adjusting the positions of the standard mirror (16) and the sample to be tested (17) until the light spot reflected by the standard mirror (16) and the sample to be tested (17) in the alignment camera (12) is located at the center and the light spot is the smallest; Step 2, adjusting the distance d1 between the polarization beam splitter prism (3) and the first plane reflector (5), the distance d2 between the polarization beam splitter prism (3) and the second plane reflector (7), and the distance d3 between the standard mirror (16) and the sample to be measured (17) so that d1+d3=d2; Step 3, adjusting the position of the 1× relay lens (21) to ensure that the two beams of light emitted from the Wollaston prism (19) at a certain angle can completely enter the 1× relay lens group (21); at the same time, adjusting the positions of the second polarizer (22) and the imaging camera (23) until the interference pattern appears on the imaging camera (23).

Images